1. Field of the Invention
This invention relates to an automatic equalization system for suppressing errors in a transmitted digital information signal. Also, this invention relates to a noise reduction circuit. Furthermore, this invention relates to a phase lock control circuit.
2. Description of the Related Art
It is known to transmit digital video and audio information signals via limited frequency bands. Also, it is known to reproduce digital video and audio information signals from recording mediums. The rate of errors in such a digital information signal tends to be adversely affected by noise. In addition, the rate of errors depends on the characteristic of a transmission path, the type of a recording medium, or the type of transmission.
There are prior-art automatic equalization systems of various types which operate to suppress errors in transmitted digital information signals. The prior-art automatic equalization systems implement level control, bit synchronization control, and waveform equalization. The level control adjusts the maximum level of signal samples at a given level to enable accurate detection of values represented by a transmitted digital information signal. The bit synchronization control adjusts a sampling clock signal into timing agreement with moments at which data bits are present. The waveform equalization compensates for deteriorations in high frequency components and low frequency components of a transmitted digital information signal, and also for inter-symbol interferences.
Generally, calibration and adjustment of portions of the prior-art automatic equalization systems are relatively complicated.